Elastic bladder and battery cell assemblies including same

ABSTRACT

A battery pack includes a battery housing and electrochemical cells disposed in the battery housing in a stacked configuration. Elastic bladders are disposed between adjacent cells of a cell stack. The elastic bladders are configured to serve as a compression spring that provide a predetermined compression force to each cell while accommodating cell growth during use. The elastic bladders may include surface features such as strategically shaped and/or located protrusions or restrained regions that are configured to permit compliance and can be tuned to address the requirements of a specific application and permit application of varying stiffness characteristics across a surface of a cell.

BACKGROUND

1. Field of the Invention

The present application relates to battery packs formed of electricallyinterconnected cells, and in particular, to lithium (e.g., lithium-ion,lithium-polymer, etc.) cells arranged into modules with elastic bladderelements interposed with the cells.

2. Description of the Related Art

Battery packs provide power for various technologies ranging fromportable electronics to renewable power systems and environmentallyfriendly vehicles. For example, hybrid electric vehicles (HEV) use abattery pack and an electric motor in conjunction with a combustionengine to increase fuel efficiency. Battery packs are formed of aplurality of electrochemical cells. Although nickel metal hydride(Ni-MH) cells are commonly used to form battery packs for HEVapplications, lithium-ion (Li-ion) cells are increasingly used in HEVapplications since they provide roughly twice the power and energydensity of a Ni-MH cell.

Lithium-ion cells are sometimes provided in a cell housing having acylindrical or prismatic (rectangular) shape. Alternatively, such cellsmay be in the form of a so-called pouch cell. Regardless of shape, thecell may include electrodes (for example, a cathode, an anode and anintermediate separator provided in a stacked arrangement) that arerolled in the form of a so-called jelly roll and are placed in the cellhousing along with an electrolyte.

To construct a power-producing electrical system, multiple cells arearranged in stacks and are connected electrically in series or inparallel. The voltage of the cell is dependent on the cell chemistry,the current is dependent on the rate of ion transfer between the cathodeand anode, and the capacity depends on the total surface area of thecell. To maintain cell capacity over the life of the cell, it isimportant to maintain a uniform distribution of pressure across asurface of the cell.

However, some cell configurations are subject to cyclical changes involume as a consequence of variations in the state of charge of thecell. For example, in some instances, the total cell volume may vary asmuch five to six percent or more during charge and discharge cycling.Thus a need exists for a module assembly structure that can accommodatetime-varying cell dimensional changes as well as provide a specifiedcompression force to each cell.

SUMMARY

In some aspects, a battery stack includes a first cell, and a secondcell positioned adjacent the first cell in a stacked arrangement withthe first cell. The first and second cells each include a cell housing,a positive electrode, and a negative electrode. The positive electrodeand the negative electrode are sealed within the cell housing along withan electrolyte. The battery stack includes an elastic member disposedbetween the first cell and the second cell. The elastic member includesa first sheet, and a second sheet layered with the first sheet. Thefirst sheet and the second sheet are joined along a first sealed linethat forms a peripheral edge of the elastic member, and the first sheetand the second sheet are joined along a second sealed line that isspaced apart from the peripheral edge, the second sealed line forming aclosed shape. A first interior space is defined between the first sheet,the second sheet, the first sealed line and the second sealed line. Inaddition, a second interior space is defined between the first sheet,the second sheet and within the second sealed line. One of the firstinterior space and the second interior space is at least partiallyinflated, and the other of the first interior space and the secondinterior space is less inflated than the one of the first interior spaceand the second interior space.

In some aspects, a battery module includes a cell support element; afirst cell supported on the cell support element, and a second cellsupported on the cell support element. The second cell is positionedadjacent the first cell in a stacked arrangement with the first cell.The first and second cells each include a cell housing, a positiveelectrode, and a negative electrode. The positive electrode and thenegative electrode are sealed within the cell housing along with anelectrolyte. The battery module includes an elastic member disposedbetween the first cell and the second cell. The elastic member includesa first sheet, and a second sheet layered with the first sheet. Thefirst sheet and the second sheet are joined along a first sealed linethat forms a peripheral edge of the elastic member, and the first sheetand the second sheet are joined along a second sealed line that isspaced apart from the peripheral edge, the second sealed line forming aclosed shape. A first interior space is defined between the first sheet,the second sheet, the first sealed line and the second sealed line. Inaddition, a second interior space is defined between the first sheet,the second sheet and within the second sealed line. One of the firstinterior space and the second interior space is at least partiallyinflated, and the other of the first interior space and the secondinterior space is less inflated than the one of the first interior spaceand the second interior space.

In some aspects, a battery pack includes a battery pack housing; a firstcell disposed in the housing, and a second cell disposed in the housing.The second cell is positioned adjacent the first cell in a stackedarrangement. The first and second cells each include a cell housing, apositive electrode, and a negative electrode. The positive electrode andthe negative electrode are sealed within the cell housing along with anelectrolyte. The battery pack includes an elastic member disposedbetween the first cell and the second cell. The elastic member includesa first sheet, and a second sheet layered with the first sheet. Thefirst sheet and the second sheet are joined along a first sealed linethat forms a peripheral edge of the elastic member, and the first sheetand the second sheet are joined along a second sealed line that isspaced apart from the peripheral edge, the second sealed line forming aclosed shape. A first interior space is defined between the first sheet,the second sheet, the first sealed line and the second sealed line. Inaddition, a second interior space is defined between the first sheet,the second sheet and within the second sealed line. One of the firstinterior space and the second interior space is at least partiallyinflated, and the other of the first interior space and the secondinterior space is less inflated than the one of the first interior spaceand the second interior space.

The battery stack, the battery module and/or the battery pack mayinclude one or more of the following features: The first interior spaceis at least partially inflated and the second sealed line surrounds anopening in the elastic element. The second interior space is at leastpartially inflated and the first interior space lacks inflation. Thefirst sheet and the second sheet are joined along second sealed linesthat are spaced apart from the common peripheral edge, each secondsealed line defining a second interior space, wherein all of the all ofthe second interior spaces have the same shape. The first sheet and thesecond sheet are joined along second sealed lines that are spaced apartfrom the common peripheral edge, each second sealed line defining asecond interior space, wherein all of the all of the second interiorspaces have the same size. The second interior spaces are distributeduniformly across an area defined by the peripheral edge. The secondinterior spaces are concentrated in a central region of an area definedby the peripheral edge. The elastic member is configured to apply acompression force to a surface of the cell housing of each of the firstcell and the second cell. The elastic member is configured such that theapplied compression force is greater in a central region of the surfacethan in a peripheral region of the surface. The elastic member is freeof a fluid inlet and a fluid outlet.

In some aspects, a battery module includes a stacked arrangement ofprismatic lithium-ion cells with interposed elastic members that aredesigned to accommodate cyclic volumetric expansion of the cell as wellas provide a specified compression force to each cell.

The elastic members can be manufactured using common and relatively lowcost manufacturing processes including, but not limited to, metalstamping, plastic sheet forming, sheet welding to form fluid filledbladders, etc. In addition, the elastic members provide a low-cost,light-weight compliant structural member in the battery module thatpermits cell growth while maintaining a required cell compression forceover the life of the battery in order to enable maximizing the lifetimeof the battery cell.

In some embodiments, the elastic member is formed of two sheets ofmaterial that are bonded together along one or more sealed lines orotherwise connected at strategic locations, and filled with fluid toform an elastic bladder. The elastic bladder is used as a compressionspring between adjacent battery cells. The elastic bladder uses thecompression of the fluid and the resiliency and elasticity of the sheetsof material to provide a predictable compression force on the cells.

The elastic members are fluid-filled bladders that include features suchseal lines that form restrained regions defining protrusions thatcontact the cell housing when the elastic member is positioned adjacentthe cell. In some embodiments, the protrusions may be equallydistributed about a surface of the elastic member so as to provide auniformly distributed compression force to the cell surface. In otherembodiments, the elastic member may have protrusions that arestrategically arranged over a surface of the cell to accommodate cellhousing expansion. For example, in cases where the expansion of theprismatic cell housing is non-uniform across a surface of the cell, theprotrusions may be unequally distributed over the surface of the elasticmember. In some embodiments, the number of protrusions and/or thestiffness of the protrusions is increased in a central region of theelastic member relative to a peripheral region of the elastic member toaddress relatively larger expansion in a central region of the surfaceof the cell. The stiffness of the elastic member may be adjusted bychanging a size and/or geometry of the protrusions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a battery pack.

FIG. 2 is a perspective view of an elastic member disposed between twocells.

FIG. 3 is a cross-sectional view of the elastic member of FIG. 2.

FIG. 4 is a schematic view of a cell stack with elastic membersinterposed between adjacent cells.

FIG. 5 is a schematic view of a cell stack with elastic membersinterposed between adjacent cells and disposed on each end of the cellstack.

FIG. 6 is a perspective view of another embodiment elastic memberdisposed between adjacent cells.

FIG. 7 is a cross-sectional view of the elastic member of FIG. 6.

FIG. 8 is a perspective view of another embodiment elastic member.

FIG. 9 is a cross-sectional view of the elastic member of FIG. 8 as seenalong line 9-9 of FIG. 8.

FIG. 10 is a perspective view of another embodiment elastic member.

FIG. 11 is a cross sectional view of the elastic member of FIG. 10 asseen along line 11-11 of FIG. 10.

FIG. 12 is a perspective view of the elastic member of FIG. 10 in apartially folded configuration.

FIG. 13 is a perspective view of another embodiment elastic member.

FIG. 14 is a cross-sectional view of the elastic member of FIG. 13 asseen along line 14-14 of FIG. 13.

FIG. 15 is a schematic illustration of an alternative arrangement of theprotruding regions of FIG. 13.

FIG. 16 is a schematic illustration of another alternative arrangementof the protruding regions of FIG. 13.

FIG. 17 is a schematic illustration of another alternative arrangementof the protruding regions of FIG. 13.

FIG. 18 is a schematic illustration of another alternative arrangementof the protruding regions of FIG. 13.

FIG. 19 is a perspective cross-sectional view of another embodimentelastic member.

FIG. 20 is a schematic illustration of an alternative arrangement of theprotruding regions of FIG. 19.

FIG. 21 is a schematic illustration of another alternative arrangementof the protruding regions of FIG. 19.

FIG. 22 is a perspective view of another embodiment elastic member.

FIG. 23 is a perspective view of another embodiment elastic member.

DETAILED DESCRIPTION

Referring to FIG. 1, a battery pack 10 used to provide electrical powerincludes prismatic electrochemical cells 20 that are electricallyinterconnected and stored in an organized manner within a battery packhousing 12. The term “prismatic” as used herein refers to having arectangular shape. The cells 20 are arranged in a side-by-sideconfiguration to form a stack 18, and several cells 20 in the stackedarrangement are bundled together to form a battery module 15. Within thebattery module 15, the stacked group of cells 20 may be commonlysupported on a support plate 17 and bound together under compression viaa band 16. Although the illustrated embodiment of the battery module 15includes six cells 20, battery modules 15 may include a greater or fewernumber of cells 20. Several battery modules 15 are collected intosubunits 14, and several subunits 14 are arranged within the batterypack housing 12. An elastic member 30 is disposed between each cell 20of the stack 18 to maintain a compression force on the cells 20 and toallow the cells 20 to expand and contract during charge and discharge ina controlled manner, as discussed further below.

The cells 20 are prismatic lithium-ion cells. Each cell 20 includes acell housing 19. An electrode assembly (not shown) is sealed within thecell housing 19 along with an electrolyte to form a power generation andstorage unit. The electrode assembly may be a “jelly roll” electrodeassembly that includes a positive electrode, a negative electrode and anintermediate separator provided in a stacked and rolled arrangement.

Each cell housing 19 includes a first side 21 and a second side 22opposed to the first side 21. The first and second sides 21, 22correspond to the broad sides of the rectangular cell housing 19. Thecell housing 19 also includes four relatively narrow end surfaces 23,24, 25, 26 that extend between the first side 21 and the second side 22.In the illustrated embodiment, a first end surface 23 and a third endsurface 25 are on opposed sides of the cell 20 and are longer than asecond end surface 24 and a fourth end surface 26. The second and fourthend surfaces 24, 26 extend perpendicular to the first and third endsurfaces 23, 25. Each cell 20 includes terminals 27, 28 that protrudefrom the first end surface 23. Each cell 20 also includes a vent 29 thatopens through the first end surface 23.

Referring to FIGS. 2-3, the elastic member 30 is a fluid-filled bladder.The elastic member 30 serves as a compression spring, and includes afirst sheet 31 and a second sheet 32 layered with the first sheet 31.The first sheet 31 and the second sheet 32 are joined along a sealedline 34 that forms a peripheral edge of the elastic member 30. Thesealed line 34 encloses an area that is the same shape as the area ofthe cell first and second sides 21, 22, and is in a range of 80 percentto 120 percent of the area of the cell first and second sides 21, 22. Insome embodiments, the sealed line 34 encloses an area that is about 100percent of the area of the cell first and second sides 21, 22. Thesealed line 34 may be formed using known methods including heating,welding or adhesives. An interior space 35 defined within the sealedline 34 is filled with a fluid such as air to an extent that the firstsheet 31 is spaced from the second sheet 32 at interior locations spacedapart from the sealed line 34. The fluid is captured within the interiorspace 35 at the time of manufacture, and the elastic member 30 is freeof fluid inlets and outlets.

Referring to FIGS. 4-5, the elastic member 30 is disposed between eachcell 20 of a stack 18 to maintain a compression force on the cells 20and to allow the cells 20 to expand and contract during charge anddischarge in a controlled manner. The elastic member 30 leverages thecompression of the fluid and the resiliency and elasticity of the sheetmaterial to provide a predictable and uniform compression force on thecells 20. For a battery module 15 containing a stack 18 of six cells 20,the battery module 15 would include five elastic members 30, one elasticmember 30 disposed between each adjacent pair of cells 20 (FIG. 4). Inother embodiments, in addition to including one elastic member 30disposed between each adjacent pair of cells 20, a battery module 15 mayalso include an elastic member 30 disposed on an outward facing side ofeach outermost cell 20 of the stack 18 (FIG. 5). In this configuration,the outermost elastic members 30 may be supported by an adjacentstructural member such as a battery module band 17, the outermost cell20 of an adjacent battery module 15, an inner surface of the batterypack housing, etc.

Referring to FIGS. 6-7, an alternative embodiment elastic member 130 isa bladder that is restrained at the perimeter and in strategic locationswithin the perimeter. For example, the elastic member 130 is formed of aplurality of fluid filled bladders 138 joined by webbing. Like theelastic member 30, the elastic member 130 serves as compression spring,and includes a first sheet 131 and a second sheet 132 layered with thefirst sheet 131. The first and second sheets 131, 132 are formed of aresilient, elastic material. The first sheet 131 and the second sheet132 are joined along a first sealed line 134 that forms a peripheraledge of the elastic member 130. The first sealed line 134 encloses anarea that is the same shape as the area of the cell first and secondsides 21, 22, and is in a range of 80 percent to 120 percent of the areaof the cell first and second sides 21, 22. In some embodiments, thefirst sealed line 134 encloses an area that is about 100 percent of thearea of the cell first and second sides 21, 22. The first sheet 131 andthe second sheet 132 are joined along a second sealed line 136 that isspaced apart from the first sealed line 134. The second sealed line 136forms a closed shape such as a circle (shown) or a rectangle. The firstand second sealed lines 134, 136 may be formed using known methodsincluding heating, welding or adhesives.

A first interior space 135 is defined between the first sheet 131, thesecond sheet 132, the first sealed line 134 and the second sealed line136. In addition, a second interior space 137 is defined between thefirst sheet 131, the second sheet 132 and within the second sealed line136. In the embodiment illustrated in FIG. 5, the second interior space137 is at least partially inflated forming the fluid filled bladder 138,and the first interior space 135 is free of inflation providing awebbing that surrounds the fluid filled bladder 138. The elastic member130 includes several uniformly and closely spaced second sealed lines136, each defining a second interior space 137 corresponding to a fluidfilled bladder 138.

In the illustrated embodiment, the fluid filled bladders 138 each havethe same shape and size, and are uniformly distributed within the areadefined by the first sealed line 134. However, the fluid filled bladders138 are not limited to this configuration. In some embodiments, thefluid filled bladders 138 are shaped, sized, and/or distributed toprovide non-uniform spring characteristics over the area defined by thefirst sealed line 134. For example, since the prismatic cell 20 tends toexperience greater distortion in a central region of the cell first andsecond sides 21, 22 relative to a periphery of the cell first and secondsides 21, 22, the elastic member 130 may be configured to provide agreater concentration of fluid filled bladders 138 in a central regionof the elastic member 130 than in a peripheral region. Alternatively, oradditionally, the elastic member 130 may be configured to provide fluidfilled bladders 130 that are more stiff in a central region than thosein a peripheral region, for example by tuning the shape and/or size ofthe fluid filled bladders 130 according to location.

In some embodiments, the first sealed line 134 is omitted, and the firstinterior space 135 is defined between the first sheet 131, the secondsheet 132, a peripheral edge of the elastic member 130 and the secondsealed line 136. In such embodiments, the first interior space 135 isopen along the peripheral edge, and is at atmospheric pressure.

Referring to FIGS. 8-9, another alternative embodiment elastic member230 is a bladder that is restrained at the perimeter and in strategiclocations within the perimeter. For example, the elastic member 230 is asingle fluid filled bladder 238 having a plurality of restrained regionswithin the perimeter. Like the elastic member 30, the elastic member 230serves as compression spring, and includes a first sheet 231 and asecond sheet 232 layered with the first sheet 231. The first and secondsheets 231, 232 are formed of a resilient, elastic material. The firstsheet 231 and the second sheet 232 are joined along a first sealed line234 that forms a common peripheral edge of the elastic member 230. Thefirst sealed line 234 encloses an area that is the same shape as thearea of the cell first and second sides 21, 22, and is in a range of 80percent to 120 percent of the area of the cell first and second sides21, 22. In some embodiments, the first sealed line 234 encloses an areathat is about 100 percent of the area of the cell first and second sides21, 22. The first sheet 231 and the second sheet 232 are joined along asecond sealed line 236 that is spaced apart from the first sealed line234. The second sealed line 236 forms a closed shape such as a circle(shown) or a rectangle and provides a restrained region 239 within thefluid filled bladder 238. The first and second sealed lines 234, 236 maybe formed using known methods including heating, welding or adhesives.

A first interior space 235 is defined between the first sheet 231, thesecond sheet 232, the first sealed line 234 and the second sealed line236. In addition, a second interior space 237 is defined between thefirst sheet 231, the second sheet 232 and within the second sealed line236. One of the first interior space 235 and the second interior space237 is at least partially inflated, and the other of the first interiorspace 235 and the second interior space 237 is less inflated than theone of the first interior space 235 and the second interior space 237.In the embodiment illustrated in FIG. 8, the first interior space 235 isat least partially inflated forming the fluid filled bladder 238, andthe second interior space 237 is free of inflation. In addition, thematerial corresponding to the second interior space 237 may be removed,forming openings 240 in the elastic member 230. In other embodiments(not shown), the material corresponding to the second interior space 237remains intact and may lack inflation. The elastic member 230 includesseveral uniformly spaced second sealed lines 236, each defining a secondinterior space 237 corresponding to a restrained region 239.

In the illustrated embodiment, the restrained regions 239 each have thesame shape and size, and are uniformly distributed within the areadefined by the first sealed line 234. However, the restrained regions239 are not limited to this configuration. In some embodiments, therestrained regions 239 are shaped, sized, and or distributed to providenon-uniform spring characteristics over the area defined by the firstsealed line 234. For example, the elastic member 230 may be configuredto provide a greater concentration of the restrained regions 239 in acentral region of the elastic member 230 than in a peripheral region.Alternatively, or additionally, the elastic member 230 may be configuredto be more stiff in a central region than those in a peripheral region,for example by tuning the shape and/or size of the restrained regions239 according to location.

The first and second sheets 31, 32, 131, 132, 231, 232 are formed of aresilient, elastic material. For example, the material used to form thefirst and second sheets may selected from the group including, but notlimited to, rubber (natural rubber based material), elastomer (syntheticrubber material), and polymer (plastic).

Referring to FIGS. 10-12, another alternative embodiment elastic member330 is a bladder that is formed of a pair of plate portions 331, 332that cooperate to form a bellows-type compression spring. The firstplate portion 331 is substantially similar in form to the second plateportion 332, whereby only the first plate portion 331 will be describedin detail, and common reference numbers will be used to refer to commonelements.

The first plate portion 331 is rectangular in size and shape to conformto the size and shape of the cell first and second sides 21, 22. Thefirst plate portion 331 defines a plane 335 and includes offset regions337, 339 that are non-coplanar with the plane 335. In particular, thefirst plate portion 331 includes a peripheral flange 337 that is offsetfrom and parallel to the plane 335. The flange 337 surrounds aperipheral edge 336 of the first plate portion 331. In addition, thefirst plate portion 331 includes a protrusion 339 that protrudes fromthe plane 335 a distance corresponding to the offset of the flange 337,and in the same direction as the offset of the flange 337. Theprotrusion 339 is a single protrusion that is centered within the areadefined by the peripheral edge 336 of the first plate portion 331.

The second plate portion 332 is layered with the first plate portion 331in a stacked configuration. In addition, the second plate portion 332 isarranged in a mirrored orientation relative to the first plate portion331 so that the first plate portion flange 337(1) contacts the secondplate portion flange 337(2), the first plate portion protrusion 339(1)contacts the second plate portion protrusion 339(2), and the first plateportion plane 335(1) is spaced apart from the second plate portion plane335(2). This configuration forms a bellows that allows for compliancewhen the elastic member 330 is disposed between adjacent cells 20. Inaddition, the central protrusions 339(1), 339(2) provide some stiffnessto the bellows arrangement, which can be adjusted by adjusting the shapeand/or size of the protrusions 339(1), 339(2).

Although the embodiment illustrated in FIGS. 10-12 includes plateportions 331, 332 having a single protrusion 339(1), 339(2) that iscentered within a periphery of the respective plate portion 331, 332,the elastic member 330 is not limited to having a single, centeredprotrusion 339(1), 339(2). For example, in some embodiments, the elasticmember 330 includes plate portions 331, 332 having multiple protrusions339(1), 339(2) that are uniformly distributed across an area surroundedby the respective flanges 337(1), 337(2). In other embodiments, theelastic member 330 includes plate portions 331, 332 having multipleprotrusions 339(1), 339(2) that are concentrated in a central region ofthe area surrounded by the respective flanges 337(1), 337(2).

In some embodiments, the first plate portion 331 is formed separatelyfrom, and is not joined to, the second plate portion 332. As a result,the first plate portion 331 is movable relative to the second plateportion 332.

In other embodiments, the first plate portion 331 is formed separatelyfrom, and is subsequently joined to, the second plate portion 332. Forexample, the first plate portion 331 may be connected to the secondplate portion 332 along all contacting surfaces (e.g., along the flange337 and protrusion 339), or alternatively, at strategic portions of thecontacting surfaces for example in a spot welding process. As a result,the contacting surfaces of first plate portion 331 are fixed relative tothose of the second plate portion 332.

In still other embodiments, the first plate portion 331 is formed alongwith the second plate portion 332 from a single piece of material, forexample in a stamping operation. In this embodiment, the first plateportion 331 shares a portion of a peripheral edge 336 with the secondplate portion 332. The shared edge portion serves as a fold line 340,and in use the elastic member 330 is folded along the fold line 340 sothat the first plate portion 331 overlies the second plate portion 332(see FIG. 12, which illustrates a partially folded configuration of theelastic member 330).

Referring to FIGS. 13-14, another alternative embodiment elastic member430 is a plate (e.g., a single-thickness sheet) that is formed having acurved or wavy contour when seen in cross-section Like the previouslydescribed embodiments, the elastic member 430 serves as compressionspring. The elastic member 430 defines a continuous (e.g.,non-perforated) surface that conforms to the shape and size of the cellfirst and second sides 21, 22. In particular, the elastic member 430includes a first side 431, and a second side 432 that is opposed to thefirst side 431. The elastic member 430 includes an array of firstprotruding regions 433 and an array of second protruding regions 434.Each first protruding region 433 is a protrusion that protrudesoutwardly from the first side 431 and coincides with a depression formedin the second side 432. Similarly, each second protruding region 434 isa protrusion that protrudes outwardly from the second side 432 thatcoincides with a depression formed in the first side 434.

The elastic member 430 generally resides within a plane 435. The firstprotruding regions 433 protrude out of the plane 435 in a firstdirection (e.g., in a direction normal to the first side 431), and thesecond protruding regions 434 protrude out of the plane 435 in adirection opposed to the first direction. The first protruding regions433 and the second protruding regions 434 are spaced apart from eachother, and the portions of the elastic member 430 intermediate theprotruding regions 433, 434 reside in the plane 435, and are referred toas “intermediate regions” 436.

In some embodiments, the first protruding regions 433 are arranged in agrid pattern defined by rows and columns, and each second protrudingregion 434 is disposed along the rows and columns so as to alternatewith adjacent first protruding regions. This configuration is shownschematically in FIG. 15, in which an “o” represents a first protrudingregion 433, and an “x” represents a second protruding region 434.

Referring to FIG. 16, in other embodiments, the first protruding regions433 are arranged in a grid pattern defined by rows and columns, and eachsecond protruding region 434 is disposed in an interstitial spacebetween adjacent first protruding regions 433.

In the embodiments illustrated in FIGS. 13-16, the first and secondprotruding regions 433, 434 are uniformly distributed across an areasurrounded by the elastic member periphery. In other embodiments, theelastic member 430 includes first and second protruding regions 433, 434that are concentrated in a central region of the area surrounded byelastic member periphery in order to provide relatively increasedstiffness in this region. The non-uniform distribution of the first andsecond protruding regions 433, 434, in which the density of firstprotruding regions 433 and second protruding regions 434 is greater in acentral region of the elastic member 430 than in a periphery of theelastic member 430, can be accomplished, for example by arranging asubset of the first protruding regions 433 in an alternating manneralong a line with a subset of the second protruding regions 434. In someembodiments, the line is linear (FIG. 17), whereas in other embodiments,the line is curved (FIG. 18).

As an alternative to, or in addition to, adjusting the spring stiffnessof the elastic member 430 by varying the distribution of the protrudingregions 433, 434, it is possible to adjust the spring stiffness of theelastic member 430 by varying the shape of the protruding regions 433,434. In the illustrated embodiments, the protruding regions 433, 434 aregenerally rectangular with sidewalls 437 that are generallyperpendicular to the plane 435. The spring rate of the elastic member430 can be decreased, for example, by providing protruding regions 433,434 having sidewalls 437 that are less perpendicular to the plane 435.In other embodiments, the protruding regions 433, 434 have acylindrical, conical or other shape. In addition, and/or alternatively,by providing an elastic member in which the geometry of the protrusions433, 434 varies across the area surrounded by the elastic memberperiphery, the spring rate of the elastic member can be made to varyacross the area surrounded by the elastic member periphery.

Referring to FIGS. 19-20, another alternative embodiment elastic member530 is a plate (e.g., a single-thickness sheet) that is formed having acurved or wavy contour when seen in cross-section Like the previouslydescribed embodiments, the elastic member 530 serves as compressionspring. The elastic member 530 defines a continuous (e.g.,non-perforated) surface that conforms to the shape and size of the cellfirst and second sides 21, 22. In particular, the elastic member 530includes a first side 531, and a second side 532 that is opposed to thefirst side 531. The elastic member 530 includes an array of protrudingregions 533 that protrude outwardly from the second side 532 andcoincides with a depression formed in the first side 531.

The elastic member 530 generally resides within a plane 535. Theprotruding regions 533 are annular and arranged concentrically, andprotrude out of the plane 535 in a direction normal to the second side532. In some embodiments, the annular, concentric protruding regions 533are arranged in a uniformly distributed pattern within the areasurrounded by the elastic member periphery, for example by providingequal spacing between adjacent protruding regions 533 a, 533 b (FIG.20). In other embodiments, the annular, concentric protruding regions533′ are arranged in a non-uniformly distributed pattern within the areasurrounded by the elastic member periphery by providing unequal spacingbetween adjacent protruding regions 533 a′, 533 b′. For example, theannular protruding regions 533 a′, 533 b′ may more closely spaced in acentral region of the elastic member relative to annular protrudingregions 533 c′ in the periphery in order to provide relatively increasedstiffness in the central region (FIG. 21).

Referring to FIGS. 22-23, another alternative embodiment elastic member630 is a plate (e.g., a single-thickness sheet) that is formed having acurved or wavy contour when seen in cross-section and that conforms tothe shape and size of the cell first and second sides 21, 22. Like thepreviously described embodiments, the elastic member 630 serves ascompression spring. The elastic member 630 includes a first side 631,and a second side 632 that is opposed to the first side 631. The elasticmember 630 includes an array of first protruding regions 633 and anarray of second protruding regions 634. Each first protruding region 633is a protrusion that protrudes outwardly from the first side 631 andcoincides with a depression formed in the second side 532. Similarly,each second protruding region 634 is a protrusion that protrudesoutwardly from the second side 532 that coincides with a depressionformed in the first side 634.

The elastic member 630 generally resides within a plane 635. The firstprotruding regions 633 protrude out of the plane 635 in a firstdirection (e.g., in a direction normal to the first side 631), and thesecond protruding regions 634 protrude out of the plane 635 in adirection opposed to the first direction. The first protruding regions633 and the second protruding regions 634 are spaced apart from eachother, and the portions 636 of the elastic member 630 intermediate theprotruding regions 633, 634 reside in the plane 635.

Unlike the wavy contoured sheets illustrated in FIG. 13-21, the elasticmember 630 has a perforated surface. In particular, The elastic member630 includes perforations (e.g., elongated, linear openings or slits)638 that are formed along a transition between intermediate (e.g.in-plane) portions 636 of the elastic member 630 and the firstprotruding regions 633 and along a transition between intermediateportions 636 of the elastic member 630 and the second protruding regions634. The perforations 638 are formed on opposed sides of each of thefirst protruding regions 633 and the second protruding regions 644. Byproviding an elastic member 630 in which the protruding regions areassociated with perforations 638, the elastic member 630 may havereduced weight and increased compliance relative to a continuous elasticmember such as is illustrated in FIG. 13.

In some embodiments, the elastic member 630 may be slightly pleated inan accordion manner. The first protruding regions 633 and the secondprotruding regions 634 are arranged on alternating fold lines 639 of thepleat, and the perforations 638 are slits that extend transverselyacross the fold lines 639 of the pleat. In these embodiments, the firstand second protrusions 633, 634 have a profile corresponding to atriangular prism (FIG. 22).

In some embodiments, the elastic member 630′ may be corrugated (e.g.,may have alternating ridges 641 and grooves 640). The first protrudingregions 633′ and the second protruding regions 634′ are arranged onalternating grooves 640, and the perforations 638′ are slits that extendtransversely across the grooves 640. In the corrugated embodiment, thefirst and second protrusions 633′, 634′ have a profile corresponding toa trapezoid (FIG. 20) and protrude outwardly relative to the ridges 641.

The plates, including the first plate portion 331, the second plateportion 332, and those used to form elastic members 430, 530, 630 areformed of a material that is sufficiently elastic to serve as acompression spring and sufficiently rigid and plastic to permit shapingin a press. For example, the material used to form the first plateportion may selected from the group including, but not limited to, metal(steel, aluminum, copper, etc.), polymer (plastic), and elastomer(synthetic rubber material).

Although the cell 20 is described herein as having a prismatic shape,the cell 20 is not limited to this shape. For example, the cell may havea circular, elliptical, pouch or other shape.

Although the cell 20 is described herein as being a lithium-ion cell,the cell 20 is not limited to this type. For example, the cell 20 may bean alkaline cell, aluminum-ion cell, nickel metal hydride cell or othertype of cell.

The elastic members 30 are not limited to use between adjacent cells 20a, 20 b, and may be adapted to provide support and compliance betweenadjacent modules 15 and/or subunits 14, and may also be adapted topermit support and compliance between a cell 20, a module 15 or asubunit 14 and the battery pack housing 12.

The elastic members 30 may include the two sheets of material 31, 131,231 and 32, 132, 232 that may be joined at strategic locations usingsealed lines 34, 134, 136, 234, 236 formed using known methods includingheating, welding or adhesives. In alternative embodiments, the twosheets of material 31, 131, 231 and 32, 132, 232 may be joined via anintermediate structure such as webbing.

Selective illustrative embodiments of the elastic member are describedabove in some detail. It should be understood that only structuresconsidered necessary for clarifying the elastic member have beendescribed herein. Other conventional structures, and those of ancillaryand auxiliary components of the battery system, are assumed to be knownand understood by those skilled in the art. Moreover, while workingexamples of the elastic member been described above, the elastic memberis not limited to the working examples described above, but variousdesign alterations may be carried out without departing from the deviceas set forth in the claims.

What is claimed, is:
 1. A battery stack comprising a first cell, asecond cell positioned adjacent the first cell in a stacked arrangementwith the first cell, the first and second cells each including a cellhousing, a positive electrode, and a negative electrode, the positiveelectrode and the negative electrode sealed within the cell housingalong with an electrolyte, and an elastic member disposed between thefirst cell and the second cell, the elastic member comprising a firstsheet, a second sheet layered with the first sheet, wherein the firstsheet and the second sheet are joined along a first sealed line thatforms a peripheral edge of the elastic member, the first sheet and thesecond sheet are joined along a second sealed line that is spaced apartfrom the peripheral edge, the second sealed line forming a closed shape,a first interior space is defined between the first sheet, the secondsheet, the first sealed line and the second sealed line, a secondinterior space is defined between the first sheet, the second sheet andwithin the second sealed line, and one of the first interior space andthe second interior space is at least partially inflated, and the otherof the first interior space and the second interior space is lessinflated than the one of the first interior space and the secondinterior space.
 2. The battery stack of claim 1, wherein the firstinterior space is at least partially inflated and the second sealed linesurrounds an opening in the elastic element.
 3. The battery stack ofclaim 1, wherein the second interior space is at least partiallyinflated and the first interior space lacks inflation.
 4. The batterystack of claim 1, wherein the first sheet and the second sheet arejoined along second sealed lines that are spaced apart from the commonperipheral edge, each second sealed line defining a second interiorspace, wherein all of the all of the second interior spaces have thesame shape.
 5. The battery stack of claim 1, wherein the first sheet andthe second sheet are joined along second sealed lines that are spacedapart from the common peripheral edge, each second sealed line defininga second interior space, wherein all of the all of the second interiorspaces have the same size.
 6. The battery stack of claim 1, wherein thesecond interior spaces are distributed uniformly across an area definedby the peripheral edge.
 7. The battery stack of claim 1, wherein thesecond interior spaces are concentrated in a central region of an areadefined by the peripheral edge.
 8. The battery stack of claim 1, whereinthe elastic member is configured to apply a compression force to asurface of the cell housing of each of the first cell and the secondcell.
 9. The battery stack of claim 8, wherein the elastic member isconfigured such that the applied compression force is greater in acentral region of the surface than in a peripheral region of thesurface.
 10. The battery stack of claim 1, wherein the elastic member isfree of a fluid inlet and a fluid outlet.
 11. A battery modulecomprising a cell support element; a first cell supported on the cellsupport element, a second cell supported on the cell support element,the second cell positioned adjacent the first cell in a stackedarrangement with the first cell, the first and second cells eachincluding a cell housing, a positive electrode, and a negativeelectrode, the positive electrode and the negative electrode sealedwithin the cell housing along with an electrolyte, and an elastic memberdisposed between the first cell and the second cell, the elastic membercomprising a first sheet, a second sheet layered with the first sheet,wherein the first sheet and the second sheet are joined along a firstsealed line that forms a peripheral edge of the elastic member, thefirst sheet and the second sheet are joined along a second sealed linethat is spaced apart from the peripheral edge, the second sealed lineforming a closed shape, a first interior space is defined between thefirst sheet, the second sheet, the first sealed line and the secondsealed line, a second interior space is defined between the first sheet,the second sheet and within the second sealed line, and one of the firstinterior space and the second interior space is at least partiallyinflated, and the other of the first interior space and the secondinterior space is less inflated than the one of the first interior spaceand the second interior space.
 12. The battery module of claim 11,wherein the first interior space is at least partially inflated and thesecond sealed line surrounds an opening in the elastic element.
 13. Thebattery module of claim 11, wherein the second interior space is atleast partially inflated and the first interior space lacks inflation.14. The battery module of claim 11, wherein the first sheet and thesecond sheet are joined along second sealed lines that are spaced apartfrom the common peripheral edge, each second sealed line defining asecond interior space, wherein all of the all of the second interiorspaces have the same shape.
 15. The battery module of claim 11, whereinthe first sheet and the second sheet are joined along second sealedlines that are spaced apart from the common peripheral edge, each secondsealed line defining a second interior space, wherein all of the all ofthe second interior spaces have the same size.
 16. The battery module ofclaim 11, wherein the second interior spaces are distributed uniformlyacross an area defined by the peripheral edge.
 17. The battery module ofclaim 11, wherein the second interior spaces are concentrated in acentral region of an area defined by the peripheral edge.
 18. A batterypack comprising a battery pack housing; a first cell disposed in thehousing, a second cell disposed in the housing, the second cellpositioned adjacent the first cell in a stacked arrangement, the firstand second cells each including a cell housing, a positive electrode,and a negative electrode, the positive electrode and the negativeelectrode sealed within the cell housing along with an electrolyte, andan elastic member disposed between the first cell and the second cell,the elastic member comprising a first sheet, a second sheet layered withthe first sheet, wherein the first sheet and the second sheet are joinedalong a first sealed line that forms a peripheral edge of the elasticmember, the first sheet and the second sheet are joined along a secondsealed line that is spaced apart from the peripheral edge, the secondsealed line forming a closed shape, a first interior space is definedbetween the first sheet, the second sheet, the first sealed line and thesecond sealed line, a second interior space is defined between the firstsheet, the second sheet and within the second sealed line, and one ofthe first interior space and the second interior space is at leastpartially inflated, and the other of the first interior space and thesecond interior space is less inflated than the one of the firstinterior space and the second interior space.
 19. The battery pack ofclaim 18, wherein the second interior spaces are distributed uniformlyacross an area defined by the peripheral edge.
 20. The battery pack ofclaim 18, wherein the second interior spaces are concentrated in acentral region of an area defined by the peripheral edge.